[RISCV][TTI] Fix missing return in the end of function

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index 65142a0..4bcb9ac 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -964,6 +964,7 @@
     // Counts of narrow/widen instructions.
     return std::abs(PowDiff);
   }
+  return BaseT::getCastInstrCost(Opcode, Dst, Src, CCH, CostKind, I);
 }
 
 unsigned RISCVTTIImpl::getEstimatedVLFor(VectorType *Ty) {